Atomic theory gr 9

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Notes on Atomic theory 1800 -1913, May 24

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Atomic theory gr 9

  1. 1. ATOMIC THEORY Lewis
  2. 2. 1700’s <ul><li>• In the 1700’s scientist agreed that elements could not be broken down. </li></ul><ul><li>• 30 +/- elements identified or known </li></ul><ul><li>• Belief that elements could be mixed together to form compounds </li></ul>
  3. 3. 1808 - John Dalton <ul><li>• Dalton proposed an Atomic Theory </li></ul><ul><li>to explain chemical reactions. </li></ul><ul><li>• He envisioned the ATOM . </li></ul><ul><li>* smallest particles of an element </li></ul><ul><li>* smooth solid sphere </li></ul><ul><li>* no electrical charge </li></ul><ul><li>• there was a belief that atoms and molecules were thought to be the same until Dalton. </li></ul><ul><li>• Scientists now believed that 2 or more </li></ul><ul><li>Non-Metalic atoms could be combined to form compounds. </li></ul>
  4. 4. 1808 - John Dalton Theory <ul><li>• All matter was made of ATOMS - these were to small to see. </li></ul><ul><li>• Each element has its own kind of Atom with its own mass. </li></ul><ul><li>• All Atoms of a single type of element are identical. </li></ul><ul><li>• Compounds are created when atoms of different elements combine in a specific ratio. </li></ul><ul><li>• Atoms can not be created, destroyed, or subdivided during a chemical change </li></ul>
  5. 5. In the 1800’s <ul><li>• until Dalton’s work many scientists believed that molecules and atoms were the same. </li></ul><ul><li>• after Dalton it was accepted that a molecule was the combination of two or more non-metal atoms in combination. </li></ul><ul><li>• in 1830 Michael Faraday showed atoms </li></ul><ul><li>can gain electrical charges. </li></ul><ul><li>(static electricity) </li></ul>
  6. 6. Michael Faraday <ul><li>added the following to ATOMIC THEORY </li></ul><ul><li>• matter must contain positive (+) and negative (-) charges. </li></ul><ul><li>• opposite charges attract & like repel </li></ul><ul><li>• atoms combine to form the particles of a compound because of the electrical attraction between the charges atoms ( Ions ). </li></ul>
  7. 7. 1898 - J.J. Thomson <ul><li>• discovered the presence of smaller particles than the atom… the negatively charged ELECTRON, </li></ul><ul><li>• he proposed than the atom is mostly positively charged matter with small negatively charged electrons scattered randomly throughout. </li></ul><ul><li>The Plum Pudding Model </li></ul><ul><li>( or the chocolate cookie ) </li></ul>
  8. 8. Thomson’s revisions to Atomic theory <ul><li>• Atoms contain electrons. </li></ul><ul><li>• electrons have a negative charge and a very small mass. </li></ul><ul><li>• the rest of the Atom is positively charged. </li></ul><ul><li>• electrons can be added and removed. </li></ul><ul><li>( ie. Rubbing a balloon against cloth ) </li></ul>
  9. 9. Ernest Rutherford - 1911 the Canadian connection <ul><li>While at the University of McGill, Quebec, Rutherford shot alpha particles at gold foil and found that most went straight through. </li></ul><ul><li>He reasoned that most of the mass and the positive particles were at the centre of the atom… he called this the nucleus. </li></ul>
  10. 10. Ernest Rutherford Rutherford amended the Atomic Theory to include the following. <ul><li>• the Nucleus contains all of the positive charges and most of the mass. </li></ul><ul><li>• the Nucleus contains positively charged Protons and uncharged Neutrons. </li></ul><ul><li>• Neutrons have some mass, Protons have more. </li></ul><ul><li>• the Nucleus is very small. </li></ul><ul><li>• Electrons orbit the nucleus like satellites. </li></ul><ul><li>• the mass of an electron is 1/1800 of the protons. </li></ul><ul><li>• the size of an atom is determined by the size of orbit of electrons. </li></ul><ul><li>• there is empty space between the nucleus and the electrons. </li></ul>
  11. 11. <ul><li>• When Rutherford published his findings in 1912, he knew that his version of the ATOMIC THEORY already had errors and would need to be revised. </li></ul>Modern Atomic Theory

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